Sensitization of surfactants on the chemiluminescence reaction of fluorescein isothiocyanate labeled proteins

The effect of surfactants on fluorescein isothiocyanate (FITC)–bovine serum albumin (BSA)–hypochlorite (ClO⁻), FITC–human serum albumin (HSA)–ClO⁻, FITC–ovoconalbumin (OVA)–ClO⁻, FITC–hemoglobin (Hb)–ClO⁻ systems were investigated with chemiluminescence method by the reversed phase flow injection. It was found that the chemiluminescence (CL) intensity of each system was increased greatly in the presence of cationic surfactants. Cethyltrimethylammonium bromide (CTAB) is the optimal surfactant of these systems. The optimal conditions of the CL reaction and the optimal concentration of CTAB were examined and the function of cationic surfactant CTAB on the CL reaction was also discussed.     

A flow-injection chemiluminescence method for the determination of human serum albumin, using the reaction of fluorescein-human serum albumin-sodium hypochlorite by the enhancement effect of the cationic surfactant cetyltrimethylammonium bromide.

The interaction between surfactant and fluorescein was studied, using a fluorescence spectroscopy and flow-injection (FI) chemiluminescence (CL) method. It was found that the cationic surfactant cetyltrimethylammonium bromide (CTAB) could cause the structural transformation of fluorescein from the quinone to the spirolactone form, and greatly enhance the CL intensity of the fluorescein-human serum albumin (HSA) complex. Based on this finding, a rapid and sensitive FI-CL method was developed for the determination of HSA. Under the optimum conditions, the proposed method has a linear range of 0.05-24.0 microg/mL, with a detection limit of 0.03 microg/mL for HSA (3sigma). The relative standard deviation (RSD) of 1.2 microg/mL HSA (n = 8) is 0.8%. The method was applied to the determination of protein content in urine samples, with satisfactory results. Density functional theory was used to study the mechanism of surfactant-enhanced CL intensity of the fluorescein-HSA complex.     

Comparative Studies of Lipase from Rhizopus Delemar in Various Microemulsion Systems

Hydrolysis of triglycerides by lipase from Rhizopus delemar has been studied in three different types of microemulsion systems. Microemulsions were prepared by using anionic (AOT), cationic (CTAB) and nonionic (C₁₂E₄) surfactants. Various parameters affecting the reaction, such as temperature, pH optimum, water content (R = [H₂O]/[surfactant]), as well as K_m.app and V_app, were determined using triolein and tributyrin as substrates. Maximum enzyme activity was obtained at R = 9, T = 30°C and pH = 6.5 in anionic surfactant systems, while in cationic, it was found at R = 7, T = 22.5°C and pH = 5.8. The stability of the enzyme was also studied in anionic and cationic systems under various conditions. The enzymatic reaction was also found to be very slow when it was studied in the C₁₂E₄ systems.     

Sorptive affinity of ionic surfactants on silt loamy soil

Due to their broad applications, ionic surfactants have already been released into or utilized in soil and environmental systems. However, current understanding on the sorption behavior of surfactants onto soils is still limited. This work systematically investigated the sorption kinetics and isotherms of one cationic surfactant, cetyltrimethylammonium bromide (CTAB), and one anionic surfactant, sodium dodecyl sulfate (SDS), onto a silt loamy soil to determine the governing sorption mechanisms. The pseudo-second-order rate equation described the sorption kinetics data better than the pseudo-first-order rate equation. Experimental data showed that the sorption equilibrium for CTAB and SDS were reached at 24 and 240 h, respectively. Langmuir equation was better than Freundlich equation in simulating the sorption isotherms of CTAB and SDS on the soil. Soil Langmuir maximum sorption capacity of CTAB was much higher than that to SDS. When the experimental temperature increased, the sorption of CTAB and SDS on the soil decreased. In addition, the sorptive process of the surfactants on the soil was spontaneous and exothermal, as indicated by the absolute values of Gibbs free energy and enthalpy. The results also indicated that physical sorption was the dominant mechanism for the sorption of the two surfactants on the soil. Findings from this work are crucial to understand the environmental behaviors of ionic surfactants.     

Reaction mechanism of surfactant‐sensitized chemiluminescence of bis(2,4,6‐trichlorophyenyl) oxalate and hydrogen peroxide induced by gold nanoparticles

The chemiluminescence (CL) of bis(2,4,6‐trichlorophyenyl) oxalate with hydrogen peroxide in the present of cationic surfactant and gold nanoparticles was studied. The CL emission was obviously enhanced in the presence of surfactant at a suitable concentration, with a synergetic catalysis effect exhibited. Different sizes of gold nanoparticles (15 and 50 nm) showed different effects on CL intensity. Mechanisms of the CL reaction and sensitization effect are discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Spectroscopic studies on the comparative interaction of cationic single-chain and gemini surfactants with human serum albumin

To gain insights into the comparative effect of single-chain/gemini surfactants on proteins and the possible implications, the interaction of human serum albumin (HSA) with cationic single-chain surfactant cetyltrimethylammonium bromide (CTAB) and its gemini counterpart bis(cetyldimethylammonium)butane dibromide with spacer -(CH(2))(4)- (designated as G4) using turbidity measurements, far-UV and near-UV circular dichroism (CD), intrinsic fluorescence and extrinsic fluorescence spectroscopy at pH 7.0 are reported in this contribution. A decrease of 33.5% alpha-helical content at 22.5 microM G4 was monitored compared to a 15% decrease at 2,250 microM CTAB. Against a 3.5% increase at 11,250 microM CTAB, a rise of 21.1% in the alpha-helical content was observed 375 microM G4. The result is related to the stronger electrostatic and hydrophobic forces in G4, owing to the presence of two charged headgroups and two hydrophobic hydrocarbon tails that make it to bind strongly to the protein compared to its single chain counterpart, CTAB, resulting in larger unfolding. The stabilization at higher concentrations is attributed to the highly hydrophobic microdomain of the G4 aggregates formed at such concentrations. The results of the multi-technique approach are consistent with the fact that the gemini surfactants are more efficient than their conventional single-chain counterparts and hence may be used more effectively in the renaturation of proteins produced in the genetically engineered cells via the artificial chaperone protocol, as solubilizing agents to recover proteins from insoluble inclusion bodies and in drug delivery.     

Binding of cationic surfactants to DNA, protein and DNA-protein mixtures

Extent of binding (gamma 2(1)) of cationic surfactants cetyltrimethyl ammonium bromide (CTAB), myristyltrimethyl ammonium bromide (MTAB) and dodecyl trimethyl ammonium bromide (DTAB) to calf-thymus DNA, bovine serum albumin (BSA) and to their binary mixture respectively have been measured as function of bulk concentration of the surfactant by using equilibrium dialysis technique. Binding of CTAB has been studied at different pH, ionic strength (mu), temperature and biopolymer composition and with native and denatured states of the biopolymers. The chain-length of different long chain amines plays a significant role in the extent of binding under identical solution condition. The binding ratios for CTAB to collagen, gelatin, DNA-collagen and DNA-gelatin mixtures respectively have also been determined. The conformational structures of different biopolymers are observed to play significant role in macromolecular interactions between protein and DNA in the presence of CTAB. From the experimental values of the maximum binding ratio (gamma 2m) at the saturation level for each individual biopolymer, ideal values (gamma 2m)id have been theoretically calculated for binary mixtures of biopolymers using additivity rule. The protein-DNA-CTAB interaction in mixture has been explained in terms of the deviation (delta) of (gamma 2m) from (gamma 2m)id in the presence of a surfactant in bulk. The binding of surfactants to biopolymers and to their binary mixtures are compared more precisely in terms of the Gibbs' free energy decrease (-delta G degree) for the saturation of the binding sites in the biopolymers or biopolymer mixtures with the change of the bulk surfactant activity from zero to unity in the rational mole fraction scale.     

Bacterial decolorization of acid orange 7 in the presence of ionic and non-ionic surfactants

The effects of the non-ionic surfactant Triton X-100, the cationic surfactant cetyltri-methylammonium bromide (CTAB) and the anionic surfactant sodium N-lauroyl sarcosinate (SLS) on the decolorization of the reaction medium containing the monoazo dye Acid Orange 7 (AO7) by Alcaligenes faecalis and Rhodococcus erythropolis were studied. It was found that the surfactants influenced in different ways the rate of decolorization. At all concentrations tested the non-ionic surfactant Triton X-100 decreased the decolorization rate of R. erythropolis. At concentrations above the critical micelle concentration (CMC) Triton X-100 upset the usually observed exponential decay of the dye with A. faecalis due probably to the existence of an outer membrane in this organism. In concentrations above the CMC the anionic surfactant SLS inhibited the decolorization and, at prolonged incubation, caused partial release of the bound dye. The cationic surfactant CTAB in concentrations above and below the CMC accelerated drastically the binding of AO7 to the cells causing a rapid staining of the biomass and complete decolorization of the reaction medium. An attempt was made for explanation of the observed differences by the negative electrostatic charge of the living bacterial cell.     

Flow injection chemiluminescence determination of lercanidipine based on N‐chlorosuccinimide–eosin Y post‐chemiluminescence reaction

A novel post‐chemiluminescence (PCL) reaction was discovered when lercanidipine was injected into the CL reaction mixture of N‐chlorosuccinimide with alkaline eosin Y in the presence of cetyltrimethylammonium bromide (CTAB), where eosin Y was used as the CL reagent and CTAB as the surfactant. Based on this observation, a simple and highly sensitive PCL method combined with a flow injection (FI) technique was developed for the assay of lercanidipine. Under optimum conditions, the CL signal was linearly related to the concentration of lercanidipine in the range 7.0 × 10^‐10 to 3.0 × 10^‐6 g/mL with a detection limit of 2.3 × 10^‐10 g/mL (3σ). The relative standard deviation (RSD) was 2.1% for 1.0 × 10^‐8 g/mL lercanidipine (n = 13). The proposed method had been applied to the estimation of lercanidipine in tablets and human serum samples with satisfactory results. The possible CL mechanism is also discussed briefly. Copyright © 2014 John Wiley & Sons, Ltd.     

Peroxyoxalate chemiluminescence enhanced by oligophenylenevinylene fluorophores in the presence of various surfactants

The effect of several surfactants on peroxyoxalate chemiluminescence (PO‐CL) using oligophenylenevinylene fluorophores was investigated. Among several oligophenylenevinylenes consisting of stilbene units, linearly conjugated ones, such as distyrylbenzene and distyrylstilbene, effectively enhanced PO‐CL efficiency. Various effects of anionic, cationic, amphoteric and non‐ionic surfactants on the CL efficiency of PO‐CL were determined using three oxalates and the distyrylbenzene fluorophore. Anionic and non‐ionic surfactants effectively enhanced CL efficiency, in contrast to the negative effect of cationic and amphoteric surfactants. Non‐ionic surfactants were also effective in CL reactions of oxalates bearing dodecyl ester groups by the hydrophobic interaction between their alkyl chains. Considering these results, the surfactants not only increase the concentrations of water‐insoluble interacting species in the hydrophobic micelle cores, but also control rapid degradation of the oxalates by alkaline hydrolysis. Copyright © 2014 John Wiley & Sons, Ltd.     

Observation of the complex formation between Cu(II) and protein by capillary electrophoretic system incorporating an UV/CL dual detector

We investigated the complex formation between Cu(II) and human serum albumin (HSA) through a biuret reaction by use of capillary electrophoretic system incorporating an ultra-violet absorption (UV) and chemiluminescence (CL) dual detector. Cu(II)-tartrate complex and Cu(II)-human serum albumin complex were detected by UV detection (282 nm) with on-capillary, followed by CL detection (luminol-hydrogen peroxide CL reaction) with end-capillary. We examined the effects of the reaction time and temperature on the UV and CL responses. On the basis of the obtained results we considered the Cu(II)-human serum albumin complex formation processes and its catalytic activity for the CL reaction. The system easily, rapidly, and simultaneously produced useful information concerning the complex formation of Cu(II) and human serum albumin due to the presence of the both detectors.     

Coarse-grained molecular simulation of self-assembly nanostructures of CTAB on nanoscale graphene

Coarse-grained molecular dynamics simulation has been performed to study the aggregated morphology of the cationic surfactant, cetyltrimethylammonium bromide (CTAB), adsorbed on nanoscale graphene surfaces. The CTAB surfactants can self-assemble on graphene to form various supramolecular morphologies and structures. The effect of packing density, thickness of graphene sheet and width of graphene nanoribbon on the CTAB–graphene self-assembly has been investigated. The buoyant densities of various graphene–CTAB assemblies were calculated, which increase with surfactant coverage and number of graphene layers. This result demonstrates that density gradient can be used to isolate graphenes with various layers. This simulation provides larger-scale microscopic insight into the supramolecular self-assembly nanostructures for the CTAB surfactants aggregated on graphene, which could be valuable to guide fabrication of graphene-based hybrid nanocomposites.     

Effect of surfactants on stability of Acinetobacter johnsonii S35 and Oligotropha carboxidovorans S23 coaggregates

The effect of anionic (sodium dodecyl sulphate or SDS) and cationic (cetyltrimethylammonium bromide or CTAB) surfactants on the stability of binary bacterial coaggregates comprising Acinetobacter johnsonii S35 and Oligotropha carboxidovorans S23 (both sewage sludge isolates) was studied and compared with that on the complex sewage sludge flocs. Both SDS and CTAB enhanced the bacterial coaggregation at their lower concentrations of 0.2 and 0.07 mg ml(-1), respectively. However, complete deflocculation of coaggregates was observed at 1 mg ml(-1) SDS and 0.3 mg l(-1) CTAB concentrations. Further, sewage sludge flocs did not deflocculate in the presence of CTAB, although a concentration-dependent deflocculation was observed in the presence of SDS. A. johnsonii S35 and O. carboxidovorans S23 cells were separately pretreated (prior to coaggregation) with the surfactants. In spite of the partial (complete) loss of viability during SDS (CTAB) pretreatment, washed cells still retained hydrophobic character and displayed significant coaggregation (aggregation index ranging from 84% to 97% in comparison to 96% in the case of non-treated cells), demonstrating reversibility of the surfactant induced deflocculation. Further, when exposed to lower concentration of surfactants (0.2 mg ml(-1) SDS), coaggregates were more resistant (76% viability) as compared to the individual partner (S35: 52%; S23: 39% viability). Since the coaggregates are stable and provide protection from surfactants at lower concentrations (those normally expected in the sewage treatment plants), their presence as well as a sustained role in the sewage sludge bioflocculation is evident.     

DNA-surfactant interactions: coupled cooperativity in ligand binding leads to duplex stabilization.

The cooperative nature of interaction of cationic surfactants with short oligonucleotides leading to eventual stabilization of DNA duplexes is demonstrated. At submicellar concentrations and DNA:surfactant charge ratios of 0.2 to 0.8, the association of single chain (CTAB) and double chain (DOTAP) surfactants to oligonucleotides is initiated by electrostatic interaction of cationic ligands with polyanionic DNA that aligns the surfactant molecules on the DNA template. This is followed by binding of new surfactant ligands to the initial complex, driven cooperatively by the hydrophobic forces, leading to in situ formation of surfactant-bound and bare duplexes as separate species. These exhibit independent melting behaviour characterised by double transition in thermal UV profiles, with a higher T(m) for surfactant-DNA complexes. Understanding the cooperative binding of the cationic surfactants to the DNA described here may have implications for rational design of DNA binding drugs and DNA delivery systems.     

Surfactant-induced lipid peroxidation in a tropical euryhaline teleost Oreochromis mossambicus (Tilapia) adapted to fresh water

Exposure to anionic (sodium dodecyl sulfate, SDS), cationic (cetyl trimethyl ammonium bromide CTAB) and non ionic (Triton X-100) surfactants at a sub lethal concentration of 1 ppm resulted in severe oxidative stress in the hepatic, renal and cardiac tissues of fresh water adapted Oreochromis mossambicus. Hepatic catalase showed significant increase (P<0.001) in all the surfactant exposed fish, but the renal enzyme was significantly increased only in CTAB dosed fish (P<0.001) and the cardiac enzyme showed significant increase in Triton (P<0.05) and CTAB dosed fish (P<0.001). SOD levels were significantly increased (P<0.001) in hepatic, renal and cardiac tissues of all the surfactant-treated fish. Glutathione reductase also was significantly increased (P<0.001) in the hepatic and renal tissues of surfactant dosed fish except cardiac tissues of CTAB exposed animals. Glutathione levels in the tissues studied were significantly higher in the surfactant treated animals (P<0.001) whereas malondialdehyde levels were significantly elevated only in the hepatic tissues of animals exposed to Triton (P<0.001). The surfactants based on their charge, antioxidant profile and in vivo metabolism may be arranged in the order of decreasing toxicity as CTAB > Triton > SDS. Thus it may be inferred from the present study that the antioxidant defenses and the in vivo metabolism of the surfactants are key factors in deciding the surfactant toxicity.     

Selective separation of beta-lactoglobulin from sweet whey using CGAs generated from the cationic surfactant CTAB

The selective separation of whey proteins was studied using colloidal gas aphrons generated from the cationic surfactant cetyl trimethyl ammonium bromide (CTAB). From the titration curves obtained by zeta potential measurements of individual whey proteins, it was expected to selectively adsorb the major whey proteins, i.e., bovine serum albumin, alpha-lactalbumin, and beta-lactoglobulin to the aphrons and elute the remaining proteins (lactoferrin and lactoperoxidase) in the liquid phase. A number of process parameters including pH, ionic strength, and mass ratio of surfactant to protein (M(CTAB)/M(TP)) were varied in order to evaluate their effect on protein separation. Under optimum conditions (2 mmol/l CTAB, M(CTAB)/M(TP) = 0.26-0.35, pH 8, and ionic strength = 0.018 mol/l), 80-90% beta-lactoglobulin was removed from the liquid phase as a precipitate, while about 75% lactoferrin and lactoperoxidase, 80% bovine serum albumin, 95% immunoglobulin, and 65% alpha-lactalbumin were recovered in the liquid fraction. Mechanistic studies using zeta potential measurements and fluorescence spectroscopy proved that electrostatic interactions modulate only partially the selectivity of protein separation, as proteins with similar surface charges do not separate to the same extent between the two phases. The selectivity of recovery of beta-lactoglobulin probably occurs in two steps: the first being the selective interaction of the protein with opposite-charged surfactant molecules by means of electrostatic interactions, which leads to denaturation of the protein and subsequent formation and precipitation of the CTAB-beta-lactoglobulin complex. This is followed by the separation of CTAB-beta-lactoglobulin aggregates from the bulk liquid by flotation in the aphron phase. In this way, CGAs act as carriers which facilitate the removal of protein precipitate.     

Lysosomal stability in Oreochromis mossambicus (Peters) on exposure to surfactants

The three commonly used surfactants viz. anionic sodium dodecyl sulfate (SDS), cationic cetyl tri methyl ammonium bromide (CTAB) and non-ionic triton X-100 were toxic even at sub lethal levels (1 ppm for 30 days) to 0. mossambicus. Lysosomal stability index (LSI) was lowest in triton-exposed animals in vitro. In vivo, CTAB was the most toxic. SDS, the anionic surfactant was the least toxic. The possible role of surfactant structure, critical micellar concentration (CMC) and metabolism in influencing the toxicity is discussed and mechanism of action via membrane lipid peroxidation is suggested.     

Chemiluminescence determination of gemifloxacin based on diperiodatoargentate (III)‐sulphuric acid reaction in a micellar medium

A novel flow‐injection chemiluminescence (FI‐CL) analysis method for the determination of gemifloxacin in the presence of cetyltrimethylammonium bromide (CTAB) surfactant micelles is described. Strong CL signal was generated during the reaction of gemifloxacin with diperiodatoargentate (III) in a sulfuric acid medium sensitized by CTAB. Under optimum experimental conditions, the CL intensity was linearly related to the concentration of gemifloxacin from 1.0 × 10^‐9 to 3.0 × 10^‐7 g/mL and the detection limit was 7.3 × 10^‐10 g/mL (3σ). The relative standard deviation (RSD) was 1.7 % for a 3.0 × 10^‐8 g/mL gemifloxacin solution (11 repeated measurements). The proposed method was successfully applied to the determination of gemifloxacin in pharmaceutical preparations and biological fluids. The possible mechanism of the CL reaction is also discussed briefly. Copyright © 2012 John Wiley & Sons, Ltd.     

表面活性剂对琼式不动杆菌LH-1-1降解溴氰菊酯的影响

旨在探究表面活性剂对菌株降解溴氰菊酯(Deltamethrin,DM)的影响。以前期筛选到具备DM较高降解能力的Acinetobacter junii LH-1-1为目标菌株,通过荧光光谱法测定了3种不同类型表面活性剂(CTAB、AES和Tween-20)的临界胶束浓度(Critical Micelle Concentration,CMC),并探究不同表面活性剂各CMC对A.junii LH-1-1生长、DM增溶作用和菌株降解DM的影响。结果显示,测得CTAB、AES、Tween-20的CMC分别为0.793 mmol/L、0.547 mmol/L和0.031 mmol/L;CTAB对菌株的生长无明显影响,AES对菌株生长有抑制作用,Tween-20对菌株的生长有一定的促进作用;CTAB、AES和Tween-20对DM均具有较强的增溶作用;且CTAB可显著提高A.junii LH-1-1对DM的降解率,当其含量为2 CMC,72 h时DM降解率达到98.20%,较未添加表面活性剂的对照组(阳性)降解率提高了24.31%。阳离子表面活性剂CTAB可显著提高A.junii LH-1-1对DM的降解。     

Characterization of dewatering process of activated sludge assisted by cationic surfactants

In this work, the dewatering of activated sludge assisted by cationic surfactants was investigated. Dose of dodecyl trimethyl ammonium bromide (DTAB) and cetyl trimethyl ammonium bromide (CTAB) resulted in the release of extracellular polymeric substances (EPS) from sludge and decrease in sludge negative charge. The surfactants significantly promoted sludge dewaterability, as reflected by decreased specific resistance of filtration (SRF) and water content in sludge cakes. The treated sludge were analyzed by combined use of differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) analysis. CTAB was found more effective in releasing bound water from sludge than DTAB, due to its superior surface activity and strong adsorption/bridge capacities with sludge. The specific surface area and pore size of sludge cakes declined after surfactant treatment, indicating an enhanced compressibility. With these results, the surfactant-assisted dewatering mechanism could be attributed to the integrated effects of electrostatic neutralization, enhanced compaction and release of EPS and bound water. Our study clearly characterizes the accelerated dewatering process assisted by cationic surfactants, and demonstrates that cationic surfactants could be used as a potential agent for sludge dewatering.